按元素合并数组'；PHP中的父\u id

我不确定PHP中是否已经有人问过这个问题，但我找不到答案

我有一个列有id和父id的数组

$cats = [▼
  0 => array:4 [▼
    "id" => 5
    "parent_id" => 4
    "category" => "Detroit"
    "children" => []
  ]
  1 => array:4 [▼
    "id" => 4
    "parent_id" => 3
    "category" => "Michigan"
    "children" => []
  ]
  2 => array:4 [▼
    "id" => 2
    "parent_id" => 1
    "category" => "Cannes"
    "children" => []
  ]
  3 => array:4 [▼
    "id" => 1
    "parent_id" => 0
    "category" => "France"
    "children" => []
  ]
  4 => array:4 [▼
    "id" => 3
    "parent_id" => 0
    "category" => "United States"
    "children" => []
  ]
]

我想按父id向后循环，以将孙辈合并到子代中，将子代合并到父代中

我尝试使用数组搜索按id查找父对象，然后将子对象推入父对象的子对象数组

foreach ($cats as $element){
            //If not the root level
            if($element['parent_id']!==0){
                //Find parent index
                $parent_index = array_search($element['parent_id'],array_column($cats,'id'));
                //Push Child
                array_push($cats[$parent_index]['children'],$element);

            }
        }

我想我需要在将原始子元素推入父数组后取消设置它，但似乎当子元素被推入父元素时，孙子元素丢失了（正如您可以看到的，在美国[index 4]的最后一个条目中有密歇根，但没有底特律），我认为它应该在索引2中更新

array:5 [▼
  0 => array:4 [▼
    "id" => 5
    "parent_id" => 4
    "category" => "Detroit"
    "children" => []
  ]
  1 => array:4 [▼
    "id" => 4
    "parent_id" => 3
    "category" => "Michigan"
    "children" => array:1 [▼
      0 => array:4 [▼
        "id" => 5
        "parent_id" => 4
        "category" => "Detroit"
        "children" => []
      ]
    ]
  ]
  2 => array:4 [▼
    "id" => 2
    "parent_id" => 1
    "category" => "Cannes"
    "children" => []
  ]
  3 => array:4 [▼
    "id" => 1
    "parent_id" => 0
    "category" => "France"
    "children" => array:1 [▼
      0 => array:4 [▼
        "id" => 2
        "parent_id" => 1
        "category" => "Cannes"
        "children" => []
      ]
    ]
  ]
  4 => array:4 [▼
    "id" => 3
    "parent_id" => 0
    "category" => "United States"
    "children" => array:1 [▼
      0 => array:4 [▼
        "id" => 4
        "parent_id" => 3
        "category" => "Michigan"
        "children" => []
      ]
    ]
  ]
]

---

我很感激任何关于我做错了什么或为什么这不起作用的提示或答案。谢谢

每次看到任意嵌套的数组，我都会想到递归。只能通过数组中的一个循环执行此操作

这就是我的方法：在数组中循环查找子数组，并将它们附加到新数组中，第一次添加到空数组中，连续多次递归地添加到子数组中

$cats = [
  [
    "id" => 5,
    "parent_id" => 4,
    "category" => "Detroit",
    "children" => [],
  ],
  [
    "id" => 4,
    "parent_id" => 3,
    "category" => "Michigan",
    "children" => [],
  ],
  [
    "id" => 2,
    "parent_id" => 1,
    "category" => "Cannes",
    "children" => [],
  ],
  [
    "id" => 1,
    "parent_id" => 0,
    "category" => "France",
    "children" => [],
  ],
  [
    "id" => 3,
    "parent_id" => 0,
    "category" => "United States",
    "children" => [],
  ]
];

$out = [];

function get_children($in, &$out, $parent){
    foreach ($in as $item) {
        if ($parent == $item["parent_id"]){
            $out[] = $item;
            get_children($in, $out[count($out)-1]["children"], $item["id"]);
        }
    }
}

get_children($cats, $out, 0);

print_r($out);

//OUTPUT:
Array
(
    [0] => Array
        (
            [id] => 1
            [parent_id] => 0
            [category] => France
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 2
                            [parent_id] => 1
                            [category] => Cannes
                            [children] => Array
                                (
                                )

                        )

                )

        )

    [1] => Array
        (
            [id] => 3
            [parent_id] => 0
            [category] => United States
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 4
                            [parent_id] => 3
                            [category] => Michigan
                            [children] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 5
                                            [parent_id] => 4
                                            [category] => Detroit
                                            [children] => Array
                                                (
                                                )

                                        )

                                )

                        )

                )

        )

)

这可能不是最有效的解决方案，我也没有足够的知识来告诉你时间或空间的复杂性，但是，嘿，它是有效的

编辑

我后来才意识到，当您将元素添加到新数组中时，可以从原始数组中删除元素，这将使其性能更高：

function get_children(&$in, &$out, $parent){
    foreach ($in as $key=>$item) {
        if ($parent == $item["parent_id"]){
            $out[] = $item;
            unset($in[$key]);
            get_children($in, $out[count($out)-1]["children"], $item["id"]);
        }
    }
}

---

向我们显示

echo var_export（$cats）的输出因此我们可以复制粘贴和复制array（0=>array（'id'=>5，'parent'=>4，'category'=>底特律，'children'=>array（），），1=>array（'id'=>4，'parent'=>3，'category'=>Michigan'，'children'=>array（），），2=>array（'id'=>2，'parent'=>1，'category'=>Cannes'，'children=>array（），），3=>array（'id'=>1，'parent\u id'=>0，'category'=>'France'，'children'=>array（），），4=>array（'id'=>3，'parent\u id'=>0，'category'=>'us'，'children'=>array（），），）孙子在哪里？他们将在循环中创建。随着Detroit添加到Michigan，那么当.Michigan添加到美国时，Detroit将是孙子。我正在尝试将所有具有父元素的元素压缩到数组中，以便只保留父元素id为0的元素s